The invention relates to a method of operating a combustion chamber where fuel and support air are injected into a hot gas flow within a mixing zone of the combustion chamber using at least one fuel lance.
Unexamined patent application DE-A1-44 17 538 discloses a combustion chamber with self-ignition. In this combustion chamber, fuel and support air are introduced by a fuel lance into a hot gas flow, are mixed there, and the mixture is burned in a subsequent combustion zone. The fuel lance is centrally positioned in a mixing zone. The dimensions of the fuel lance are designed for approximately 10% of the total volume flow through the channel defining the mixing zone. The fuel can be injected from the centrally positioned fuel lance in a transverse direction or in the direction towards the flow. The injected fuel is carried by the vortices injected upstream along with a portion of support air over several radial openings and is mixed with the main flow. The injected fuel follows the helical course of the vortices and is evenly distributed downstream in the chamber. This reduces the risk of impacted jets on the opposing channel wall as well as the formation of xe2x80x9chot spots,xe2x80x9d as is the case in a flow without vortices.
The advantages of the central fuel injection are gained, however, at the cost of a fuel lance surface positioned in the hot gas flow that is relatively difficult to cool. This built-in element also has a substantial effect on the flow of the hot gases. For fluid flow reasons, a minimal lance length is required. This lance length furthermore requires that the fuel lance be inserted through a corresponding long hole into the burner for assembly. This creates a relatively large gap between the burner wall and fuel lance, which is relatively hard to seal. Accordingly irregular air leakages have a negative influence on the overall behavior of the burner.
In view of the above disadvantages of the prior art, the invention provides a combustion chamber and a method of operating the combustion chamber that make it possible to minimize the interference with the hot gas flow in the mixing zone of the combustion chamber. This should be accomplished along with simultaneously less cooling of the fuel lance, and an improved behavior of the combustion chamber in all load ranges should be achieved.
According to an embodiment of the invention, the fuel is injected from at least one side wall of the mixing zone of the combustion chamber. A combustion chamber according to an embodiment of the invention includes at least one fuel lance set into a side wall of the mixing zone of the combustion chamber. If desired, support air can also injected through this fuel lance.
One advantage of such a lateral, asymmetrical injection of the fuel is that the fuel lance causes only a slight interference with the flow since it is located only on the side wall of the mixing zone, and no longer centrally in the main flow. It is also advantageous if the at least one fuel lance is set into the side wall of the combustion chamber in the shape of a sphere or ellipsoid extending in the main flow direction and projecting into the interior of the mixing zone. By constructing the mixing zone as a Venturi channel or possibly additionally present built-in elements (radially or circumferentially), an increase in velocity and thus improved mixing of hot gas and fuel/support gas can be achieved. This type of arrangement practically excludes any follower areas behind the fuel lance in which fuel is able to collect.
The cooling of the fuel lance can be advantageously minimized with a reduced contact surface area between the fuel lance and the hot gas flow. The area of a seal between the sidewall of the mixing zone and the fuel lance is also kept advantageously small and in an advantageous shape.
According to a preferred embodiment of the method according to the invention, the fuel and, if desired, support air are injected in different fuel/support air mixture jets into the mixing zone of the combustion chamber. The different fuel/support air mixture jets are oriented in different directions or different sectors within the mixing zone of the combustion chamber. This embodiment is particularly advantageous because, depending on the load on the combustion chamber, jets can be added or switched off. This is also advantageous in combination with the above-mentioned built-in elements since with the targeted feeding of different sectors through the jets the fuel can be transported with the same pressure into different areas within the mixing zone.